830mV of ripple is not what we want - it doesn't look like "smoothed" pwm will do - what was the rwaw pwm ripple ,btw? I seiously doubt that this will be OK driving the LDR but an experiment is worthwhile.
What's the problem with 256 steps of pwm output - is this not enough for a 65 position vol control - what am I missing?
If PWM isn't suitable then it's a case of looking for a suitable DAC or digital pot to control the current into the LED - Paul Hynes over at DIYAudio uses DS1802 digital pot which is a double pot that can be daisy chained & is controllable via 3 wire serial interface or push button control